If the Nix daemon has never been enabled (nix.enable has always been
set to false), the gcroots directory won't exist. If the Nix daemon
is later enabled, the GC roots for booted-system and current-system
will be missing, and they might end up being garbage collected. Since
it's cheap to add GC roots even if the daemon will never be enabled,
let's just always add them so we're okay in the case where the daemon
is enabled later.
This removes `/run/nixos/activation-reload-list` (which we will need in
the future when reworking the reload logic) and makes
`/run/nixos/activation-restart-list` honor `restartIfChanged` and
`reloadIfChanged`. This way activation scripts don't have to bother with
choosing between reloading and restarting.
I was confused why I couldn't find a mention of udev.log_priority in
systemd-udevd.service(8). It turns out that it was renamed[1] to
udev.log_level. The old name is still accepted, but it'll avoid
further confusion if we use the new name in our documentation.
[1]: 64a3494c3d
most modules can be evaluated for their documentation in a very
restricted environment that doesn't include all of nixpkgs. this
evaluation can then be cached and reused for subsequent builds, merging
only documentation that has changed into the cached set. since nixos
ships with a large number of modules of which only a few are used in any
given config this can save evaluation a huge percentage of nixos
options available in any given config.
in tests of this caching, despite having to copy most of nixos/, saves
about 80% of the time needed to build the system manual, or about two
second on the machine used for testing. build time for a full system
config shrank from 9.4s to 7.4s, while turning documentation off
entirely shortened the build to 7.1s.
Add `shellDryRun` to the generic stdenv and substitute it for uses of
`${stdenv.shell} -n`. The point of this layer of abstraction is to add
the flag `-O extglob`, which resolves#126344 in a more direct way.
some options have default that are best described in prose, such as
defaults that depend on the system stateVersion, defaults that are
derivations specific to the surrounding context, or those where the
expression is much longer and harder to understand than a simple text
snippet.
